Strip tape

ABSTRACT

The present invention is drawn to a strip tape which does not undergo lowering of bonding force and which does not cause pollution of the natural environment, working environment, etc. The strip tape includes a center layer containing a polar resin, and at least one polyolefin layer laminated, via a bonding layer, on each face of the center layer. The bonding layer contains an ethylene-methacrylic acid-alkyl acrylate random copolymer. Since the strip tape includes a center layer and at least one polyolefin layer, the interlayer bonding force of the strip tape is high, the bonding strength between the center layer and the polyolefin layer can be increased, and the waterproofing property of the strip tape can be enhanced. Even when a packaging container including the strip tape is heated or cooled sharply during use, the interlayer bonding force of the strip tape is not lowered.

TECHNICAL FIELD

The present invention relates to a strip tape for a liquid foodcontainer, and more particularly to a strip tape for strongly bonding,within a packaging container for storing liquid food, overlap portionsof a packaging material.

BACKGROUND ART

Conventionally, most packaging containers for storing liquid food suchas milk, juice, liquor, cola drink, or coffee are formed by folding apackaging material prepared from a laminate including paper, plastic,metallic foil, metal-deposited film, etc., in combination. Edge portionsof the folded packaging material are overlapped with each other andwelded. In order to prevent liquid food from leaking or oozing throughthe overlap portions to the outside of the packaging container, theoverlap portions facing the interior of the packaging container arestrongly bonded together by use of a strip tape.

The strip tape is formed of, for example, a laminate including a centerlayer of a polar resin and a polyolefin layer laminated on each face ofthe center layer. When the laminate is formed, at least one of thecenter layer and the polyolefin layer is subjected to anchor coating,and then the polyolefin layer is laminated on each face of the centerlayer. Usually, a thermosetting adhesive obtained by dissolving, forexample, a polyester resin in an organic solvent is used as ananchor-coating agent for carrying out the aforementioned anchor coating.

However, when the strip tape including the center layer and thepolyolefin layer, at least one of the layers being subjected to anchorcoating, is used, liquid food is absorbed in the strip tape from an edgeportion thereof, and thus the interlayer bonding force is lowered. Whenthe packaging container is heated or cooled drastically during usethereof, the interlayer bonding force is further lowered. As a result,the center layer and the polyolefin layer exfoliate from each other,resulting in a deterioration in the function of the strip tape forprotecting liquid food contained in the packaging container. Inaddition, the strip tape having the aforementioned structure has lowthermal stability and poor oxygen-barrier property.

Moreover, since the aforementioned anchor-coating agent contains anorganic solvent, when anchor coating is carried out or when thepolyolefin layer is laminated on each face of the center layer, theorganic solvent disperses, and thus the natural environment or theworking environment is polluted.

In order to solve the aforementioned problems in relation to theconventional strip tape, an object of the present invention is toprovide a strip tape which does not undergo lowering of bonding forceand which does not cause pollution of the natural environment or theworking environment.

DISCLOSURE OF THE INVENTION

To achieve the above object, the present invention provides a strip tapecomprising a center layer formed of a polar resin, and at least onepolyolefin layer laminated, via a bonding layer, on each face of thecenter layer.

The bonding layer contains an ethylene-methacrylic acid-alkyl acrylaterandom copolymer.

Since the strip tape includes a center layer and at least one polyolefinlayer laminated, via a bonding layer, on each face of the center layer,the interlayer bonding force is high, the center layer and thepolyolefin layer can be bonded together with increased strength, and thewaterproofing property of the strip tape can be enhanced. In addition,even when a packaging container including the strip tape is heated orcooled drastically during use thereof, the interlayer bonding force isnot lowered.

When liquid food is stored in a packaging container produced by use ofthe strip tape, the liquid food stored in the packaging container can beeffectively protected, because the center layer and the polyolefin layerof the strip tape do not exfoliate from each other, and leak or oozingof the liquid food from the overlap portion of the packaging materialcan be prevented over a long period of time. The strip tape has highthermal stability and improved oxygen-barrier property.

Since the strip tape has high thermal stability and improvedoxygen-barrier property, the thickness of the strip tape can becommensurately reduced, and thus the amount of the raw material forproducing the strip tape can be reduced.

Also, since the bonding layer does not contain an organic solvent, thestrip tape does not pollute the natural environment or the workingenvironment, and the risk of fire hazards is reduced.

Moreover, since anchor coating is not carried out when the strip tape isproduced, the production process can be simplified, and high-speedproduction can be realized. In addition, the strip tape is not smudgedwith an adhesive contained in the anchor-coating agent, and otherproblems such as blocking do not arise.

In another strip tape of the present invention, the bonding layercontains an ethylene-methacrylic acid-alkyl acrylate random copolymercontaining methacrylic acid in an amount of 3-5 wt. % and an alkylacrylate in an amount of 0.05-0.2 wt. %.

In yet another strip tape of the present invention, the bonding layercontains an ethylene-methacrylic acid-alkyl acrylate random copolymerhaving a melt flow rate of 11-15 g/10 minutes, a density of 0.927-0.932g/cm³, and a Vicat softening point of 68-72° C.

In still another strip tape of the present invention, the alkyl acrylateis either methyl acrylate or ethyl acrylate.

In yet another strip tape of the present invention, the polar resin iseither an ethylene-vinyl alcohol copolymer or a polyester.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a table showing the results of measurement of the interlayerbonding strength of a strip tape.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will next be described indetail with reference to the drawing.

The strip tape of the present invention includes a center layercontaining a polar resin. Examples of the polar resin which may beemployed include ethylene-vinyl alcohol copolymers (EVOH), polyesters,vinyl acetate, ethylene-vinyl acetate copolymers, and polyamides.Particularly, ethylene-vinyl alcohol copolymers or polyesters arepreferably used.

Examples of the polyesters which may be employed include polyethyleneterephthalate (PET), polybutylene terephthalate, copolymers of ethyleneterephthalate and ethylene isophthalate, polyethylene-2,6-naphthalate,polyhexamethylene terephthalate, and copolymers of hexamethyleneterephthalate and 1,4-cyclohexanedimethylene terephthalate.

The polar resin is used without any treatment. Preferably, the polarresin is subjected to monoaxial or biaxial stretching, and is used inthe form of film having a typical thickness of about 10-50 μm. Thecenter layer may be the polar resin film, particularly a deposition filmobtained by depositing, for example, silicon oxide (SiO_(x)) or aluminumoxide (Al₂O₃) onto the face of a polyester film. When the depositionfilm is used, the oxygen barrier property of the strip tape can beenhanced.

In the manufacture of the strip tape of the present invention, bothsurfaces of the center layer are coated with polyolefin; i.e.,polyolefin layers serving as outer layers are laminated on the centerlayer. Examples of the polyolefin which may be employed includemonopolymers of ethylene or α-olefin (e.g., propylene, 1-butene,1-hexene, 4-methyl-1-pentene, or 1-octene), and copolymers of ethyleneand α-olefin. Particularly, polyethylene (e.g., low-density polyethylene(LDPE), middle-density polyethylene (MDPE), high-density polyethylene(HDPE), linear low-density polyethylene (LLDPE), or linear low-densitypolyethylene produced by use of a metallocene catalyst (mLLDPE)),polypropylene (e.g., homopolypropylene, a propylene-ethylene randomcopolymer, or a propylene-ethylene block copolymer), polybutene-1, orpoly 4-methyl-pentene-1 is preferably used.

The aforementioned linear low-density polyethylene is produced throughcopolymerization of ethylene and C4-C8 α-olefin serving as a comonomer(preferably α-olefin containing 6 or more carbon atoms, such as1-hexene, 4-methyl-1-pentene, 1-heptene, or 1-octene) in the presence ofa metallocene catalyst.

The aforementioned metallocene catalyst is a combination of metalloceneand an aluminum compound serving as a promoter, wherein metallocene is acompound having a structure in which a transition metal such astitanium, zirconium, or hafnium is sandwiched by an unsaturated cycliccompounds containing, for example, a π-electron-containingcyclopentadienyl group or a substituted cyclopentadienyl group, and thealuminum compound promoter is, for example, alkyl aluminoxane, alkylaluminum, aluminum halide, or alkyl aluminum halide. The aforementionedpolyolefin layer is preferably formed from polyethylene, particularlyfrom low-density polyethylene or linear low-density polyethylene of theaforementioned polyolefins.

The polyolefin is used without any treatment. Preferably, the polyolefinis subjected to monoaxial or biaxial stretching, and is used in the formof film having a typical thickness of about 10-200 μm. In the strip tapeof the present invention, at least one polyolefin layer is formed oneach face of the center layer. However, two or more polyolefin layersmay be formed. When two or more polyolefin layers are formed, thepolyolefin layers may be formed of identical or different materials.Also, the polyolefin layers may have the same thickness or differentthicknesses.

If necessary, a variety of additives or similar materials may be addedto at least one of the center layer and the polyolefin layer.

The strip tape of the present invention is formed by laminating at leastone polyolefin layer, via a bonding layer, on each face of the centerlayer. The bonding layer contains an ethylene-methacrylic acid-alkylacrylate random copolymer containing methacrylic acid in an amount of3-5 wt. % and an alkyl acrylate in an amount of 0.05-0.2 wt. %, andhaving a melt flow rate of 11-15 g/10 minutes (JIS K6760), a density of0.927-0.932 g/cm³ (JIS K6760), and a Vicat softening point of 68-72° C.(JIS K6760).

Examples of the alkyl acrylate which may be employed include methylacrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, and2-ethylhexyl acrylate. Particularly, methyl acrylate or ethyl acrylateis preferably used. An ethylene-methacrylic acid-alkyl acrylate randomcopolymer having the aforementioned properties is produced throughrandom copolymerization of ethylene, methacrylic acid, and an alkylacrylate by means of a customary method for producingethylene-methacrylic acid random copolymers.

No particular limitation is imposed on the method for laminating atleast one polyolefin layer, via the bonding layer, on each face of thecenter layer, and a customary lamination method is employed. Examples ofthe lamination method employed include a dry lamination method in whichat least one of a film containing the aforementioned polar resin and afilm of the aforementioned polyolefin is coated with a film serving asthe bonding layer, and the polar resin film and the polyolefin film arepress-bonded; a sandwich lamination method in which the aforementionedpolar resin and the aforementioned polyolefin are melted and extrudedfrom, for example, an extruder, and then laminated on both surfaces of afilm serving as the bonding layer; a sandwich lamination method in whichthe material of a film for forming the bonding layer is melted andextruded from, for example, an extruder, and then laminated on bothsurfaces of a film containing the aforementioned polar resin, and a filmof the aforementioned polyolefin is laminated on the extruded bondinglayer film; and a co-extrusion lamination method in which theaforementioned polar resin, the aforementioned polyolefin, and thematerial of a film for forming the bonding layer are melted andseparately extruded from dies such as flat dies or circular diesprovided in, for example, an extruder, and are laminated with oneanother.

The bonding layer typically has a thickness of 5-30 μm. Before thepolyolefin layer is laminated, via the bonding layer, on the centerlayer, at least one of the center layer and the polyolefin layer may besubjected to corona discharge treatment, in order to further increasebonding strength. The thus-formed strip tape typically has a width of4-30 mm.

As described above, since the strip tape having the aforementionedstructure includes a center layer containing a polar resin and at leastone polyolefin layer laminated, by the mediation of a bonding layer, oneach face of the center layer, the interlayer bonding force is high, thecenter layer and the polyolefin layer can be bonded together withincreased strength, and the waterproofing property of the strip tape canbe enhanced. Even when a packaging container including the strip tape isheated or cooled drastically during use of the container, the interlayerbonding force is not lowered.

When liquid food is stored in a packaging container produced by use ofthe strip tape, the liquid food stored in the packaging container can beeffectively protected, since the center layer and the polyolefin layerof the strip tape are not exfoliated from each other, and, over a longperiod of time, the liquid food never leak or ooze through the overlapportion of a packaging material. Moreover, the strip tape has highthermal stability and improved oxygen-barrier property.

Since the strip tape has high thermal stability and improvedoxygen-barrier property, the thickness of the strip tape can be reducedaccordingly, and thus the amount of the raw material for producing thestrip tape can be reduced.

Moreover, since the bonding layer does not contain an organic solvent,deterioration of the natural environment or the working environment isprevented, and the risk of fire hazards is reduced.

Furthermore, since anchor coating is not carried out when the strip tapeis produced, the production process can be simplified to thereby attainhigh-speed production. In addition, the strip tape is not smudged withan adhesive contained in an anchor-coating agent, and other problemssuch as blocking do not arise.

EXAMPLE 1

An ethylene-methacrylic acid-methyl acrylate random copolymer containingmethacrylic acid (4 wt. %) and methyl acrylate (0.1 wt. %) and having amelt flow rate of 13 g/10 minutes, a density of 0.930 g/cm³, and a Vicatsoftening point of 70° C. was melted and extruded from an extruder ontoeach face of a biaxially stretched film (thickness: 12 μm containing anethylene-vinyl alcohol copolymer, such that the thickness of theextruded film was 25 μm, and a low-density polyethylene film having athickness of 12 μm was laminated on the extruded ethylene-methacrylicacid-methyl acrylate random copolymer film, to thereby produce acomposite film.

EXAMPLE 2

A film (thickness: 15 μm) of the same ethylene-methacrylic acid-methylacrylate random copolymer as employed in Example 1 was laminated on eachface of the ethylene-vinyl alcohol copolymer film employed in Example 1.Subsequently, a linear low-density polyethylene film having a thicknessof 20 μm was laminated on the surface of the random copolymer film, tothereby produce a composite film.

EXAMPLE 3

In a manner similar to that of Example 1, the ethylene-methacrylicacid-methyl acrylate random copolymer employed in Example 1 was meltedand extruded onto each face of a biaxially stretched polyethyleneterephthalate film having a thickness of 15 μm, and a low-densitypolyethylene film having a thickness of 20 μm was laminated on theextruded ethylene-methacrylic acid-methyl acrylate random copolymerfilm, to thereby produce a composite film.

EXAMPLE 4

The procedure of Example 2 was repeated, except that a polyethyleneterephthalate film (thickness: 10 μm) on which silicon oxide wasdeposited was used instead of the ethylene-vinyl alcohol copolymer film,to thereby produce a composite film.

COMPARATIVE EXAMPLE 1

An anchor-coating agent containing a thermosetting adhesive obtained bydissolving a polyester resin in an organic solvent was applied onto eachface of the ethylene-vinyl alcohol copolymer film employed in Example 1such that the thickness of the anchor-coating film became 25 μm afterdrying, and the applied anchor-coating agent was dried. Subsequently,the low-density polyethylene film employed in Example 1 was laminated onthe anchor-coating film, to thereby produce a composite film. Duringproduction of the composite film, the organic solvent was released, andthus the working environment was considerably polluted.

COMPARATIVE EXAMPLE 2

The procedure of Example 1 was repeated, except that anethylene-methacrylic acid random copolymer containing methacrylic acid(11 wt. %) and having a melt flow rate of 8 g/10 minutes, a density of0.940 g/cm³, and a Vicat softening point of 75° C. was used instead ofthe ethylene-methacrylic acid-methyl acrylate random copolymer employedin Example 1, to thereby produce a composite film.

The results of evaluation of the strip tape will next be described.

FIG. 1 is a table showing the results of measurement of the interlayerbonding strength of the strip tape.

A test piece (i.e., strip tape) having a width of 15 mm was formed fromeach of the composite films produced in Examples 1 through 4 andComparative Examples 1 and 2, a 180-degree exfoliation test was carriedout for each test piece by use of a tensile tester at an exfoliationrate of 300 mm/minute at 23° C. and a relative humidity of 50%, tothereby measure the lamination strength between the center layer and thepolyolefin layer; i.e., interlayer bonding strength N/15 mm. The resultsare shown in FIG. 1. In FIG. 1, each value shows the average of theresults of five test pieces formed from each composite film.

A brick-shaped packaging container for storing milk (inner volume: 200ml) was formed from a packaging material formed of a laminate(low-density polyethylene film (thickness: 15 μm)/paper (basis weight:150 g/m²)/ethylene-vinyl alcohol copolymer film (thickness: 12μm)/low-density polyethylene film (thickness: 15 μm)), such that thelow-density polyethylene film laminated on the ethylene-vinyl alcoholcopolymer film provided the inner face of the container. The overlapportions of the packaging material was bonded together by use of a striptape (width: 15 mm) formed from each composite film of Examples 1through 4 and Comparative Examples 1 and 2. The thus-formed packagingcontainer was filled with water (200 ml), and then allowed to stand fortwo weeks. Thereafter, the bonding strength between the center layer andthe polyolefin layer of the strip tape, the polyolefin layer havingcontacted water, was measured in a manner similar to that describedabove. The results are shown in FIG. 1.

As shown in FIG. 1, the strip tapes produced in Examples 1 through 4have high interlayer bonding strength as compared with those produced inComparative Examples 1 and 2. In addition, the degree of lowering of theinterlayer bonding strength of the strip tapes produced in Examples 1through 4 is low even after the strip tapes are immersed in water fortwo weeks.

The present invention is not limited to the above-described embodiments.Numerous modifications and variations of the present invention arepossible in light of the spirit of the present invention, and they arenot excluded from the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a strip tape for a liquid foodcontainer.

1. A strip tape for bonding together overlap portions of packagingmaterial facing the interior surface of a packaging container, saidstrip tape comprising: (a) a center layer containing a polar resin; and(b) at least one polyolefin layer laminated, via a bonding layer on eachface of the center layer, wherein (c) the bonding layer contains anethylene-methacrylic acid-alkyl acrylate random copolymer; whereby thestrip tape comprises the structure (b)-(c)-(a)-(c)-(b) wherein layers(c) are in direct contact with layer (a), and layers (b) are in directcontact with respective layers (c); wherein the ethylene-methacrylicacid-alkyl acrylate random copolymer contains methacrylic acid in anamount of 3-5 wt.% and an alkyl acrylate in an amount of 0.05- 0.2 wt.%;and wherein the ethylene-methacrylic acid-alkyl acrylate randomcopolymer has a melt flow rate of 11-15 g/10 minutes, a density of0.927-0.932 g/cm³, and a Vicat softening point of 68-72° C.
 2. A striptape according to claim 1, wherein the alkyl acrylate is either methylacrylate or ethyl acrylate.
 3. A strip tape according to claim 1,wherein the polar resin is either an ethylene-vinyl alcohol copolymer ora polyester.
 4. A strip tape according to claim 1 wherein said centerlayer is a polyester film have a surface deposit of silicon oxide oraluminum oxide.
 5. A strip tape according to claim 1 wherein said layers(b) are the outer layers of the strip tape.
 6. A strip tape according toclaim 5 wherein said layers (b) are monoaxially or biaxially stretched.7. A strip tape according to claim 1 wherein the thickness of therespective layers are as follows: (a) is 10-50 μm; (b) is 10-200 μm; and(c) is 5-30 μm.
 8. A strip tape according to claim 1 wherein layers (c)do not contain an organic solvent.
 9. A strip tape according to claim 1having a width of 4-30 mm.
 10. A strip tape according to claim 1 whereinsaid bonding layer has a thickness of 5-30 μm.